Profile cutting machine

ABSTRACT

The contour cutting machine comprises an endless circulating bandknife ( 22 ) which is guided around bandknife pulleys ( 30-34 ). To allow adjustment of the cutting strand ( 23 ) in the Y-direction, the bandknife ( 22 ) forms two loops ( 28,36 ) merging into each other, one ( 36 ) of these two loops serving for length compensation. The bandknife pulley ( 30 ) arranged at the transition from the second loop ( 36 ) to the first loop ( 28 ) guides the bandknife ( 22 ) therearound at a looping angle of substantially 270° so that all of the bandknife pulleys ( 30-34 ) are contacted by the same surface of the bandknife ( 22 ). The bandknife ( 22 ) will always be bent in one direction only. By thus avoiding alternating bending directions, the lifespan of the bandknife ( 22 ) is lengthened.

BACKGROUND OF THE INVENTION

This invention relates to a contour cutting machine for the cutting ofobjects, such as e.g. blocks made from foamed plastic, wadding,synthetic material, rubber or cork, comprising a rotating endlessbandknife.

A contour cutting machine according to the precharacterizing part ofclaim 1 is known from DE 23 29 238 C2. This machine comprises a tablefor receiving the workpiece block, and a support arranged for verticalmovement relative to the table. On the support, vertically movablecarriages are arranged to both sides of the table. An endless bandknifeis arranged to rotate around a plurality of bandknife pulleys, whereinrespectively one bandknife pulley is located on one of the movablecarriages and the rest of the bandknife pulleys are fixed to themachine. The bandknife is guided in a closed loop, with a first portionof the loop arranged between the two vertically adjustable bandknifepulleys while forming a cutting strand in this region. The first loopportion is of a rectangular shape and has the second loop portionextending therefrom which is guided around a fifth bandknife pulley andis used for a length compensation of the bandknife in case of differentcutting heights. The fifth bandknife pulley is engaged by a tensioningdevice for setting the tension of the bandknife. On both end portions ofthe cutting strand, the respective carriages are provided with rotatingdevices for rotating the plane of the bandknife so as to change thecutting angle. In this bandknife guiding configuration comprising twoloop portions merging into each other, the bandknife has its inner sidecontacting a total of four bandknife pulleys and has its outer sidecontacting one of the bandknife pulleys. As a result, the bandknifeduring its continuous circulation is subjected to varying alternatingbending stresses which are directed both towards its inner face andtowards its outer face. Due to these alternating bending stresses incombination with the torsional stresses generated by the rotatingdevices and the tensioning of the bandknife in the longitudinaldirection, the bandknife suffers considerable mechanical stresses sothat the bandknife may undesirably break and has a reduced lifespan.

A contour cutting machine comprising a cutting wire with a similarcutting wire guiding configuration is known from GB 2 206 521 A. In thisknown machine, a cutting wire is guided to follow mutually contactingloops, thereby running around pulleys deflecting the cutting wirealternately into one direction and a direction opposite thereto.

EP-0 390 939 B1 discloses a contour cutting machine wherein thebandknife is driven to oscillate. The ends of the bandknife areconnected to a string. The bandknife and the string together form anendless loop comprising two loop portions merging into each other. Theguiding of this loop requires at least six pulleys formed as bandknifepulleys and string pulleys. Also there, the loop is guided aroundpulleys deflecting the bandknife or the string alternately into onedirection and a direction opposite thereto.

Further, DE 34 44 612 C2 discloses a contour cutting machine wherein theworkpiece table comprises two conveyor belts arranged in a common plane,which are driven synchronously and form a gap for the passage of acutting wire. The cutting wire is guided around four pulleys which arearranged on a frame adapted to be displaced and pivoted in its entirety.The cutting wire guiding path forms a single closed loop. Whenperforming a contour cutting process, the whole frame, having a largemass moment of inertia, has to be moved.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a contour cutting machinehaving an endlessly rotating bandknife, wherein only small masses needbe moved for positioning the cutting strand and wherein the bandknife issubjected to relatively small stresses and thus has a large lifespan.

In the contour cutting machine according to the instant invention, thebandknife is guided to follow two loops merging into each other andoverlapping each other on that bandknife pulley which connects theloops. The first loop is generally rectangular and comprises fourbandknife pulleys, notably two fixed bandknife pulleys and two bandknifepulleys arranged to be displaced together and having the cutting strandextending therebetween. Extending from the first loop is a second loopas a compensating loop guided around a fifth bandknife pulley. In thismanner, it is accomplished that the overall length of the bandknifestring will remain constant in each position of the displaceablebandknife pulleys. According to the invention, the bandknife is guidedat a looping angle of substantially 270° around said displaceablebandknife pulley connecting the two loops, each bandknife pulley beingcontacted by the same surface of the bandknife. In this manner, it isprovided that the bandknife throughout its circulating movement throughthe two loops will always be bent in the same direction only. Thus, noalternating bending will occur during the circulating movement of thebandknife. Since the bandknife is always bent into one direction only(and not in the opposite direction), the mechanical stress acting on thebandknife is a mere threshold stress and thus is relatively small, sothat the lifespan of the bandknife will be considerably longer than thatof a bandknife undergoing alternating bending directions.

The inventive configuration of the moving path of the bandknife isapplicable in contour cutting machines with any possible orientation ofthe cutting strand, i.e. also in machines wherein the cutting strand isoriented vertically and in machines with a horizontal cutting strand.Further, the whole worktool carrier can be arranged to be adjusted andpivoted, respectively, so that the cutting strand is arranged obliquelyto a vertical line.

An embodiment of the invention will be described in greater detailhereunder with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of the contour cutting machine,

FIG. 2 is a plan view of the machine,

FIG. 3 is a schematic view of the moving path of the bandknife in afirst position of the cutting strand,

FIG. 4 is a view of the moving path of the bandknife in a secondposition of the cutting strand, and

FIG. 5 is a view of that bandknife pulley which guides the bandknife ata large looping angle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The contour cutting machine is provided for the cutting of blocks 10 offoamed material or similar materials. The block 10 is placed onto aworkpiece carrier 11 comprising two conveyor belts 12,13 which arearranged in a common plane and can be driven in synchronism with eachother and perform a conveying motion in the direction X. Between thesuccessive conveyor belts 12,13, a gap 14 is formed for the passage ofthe bandknife. The two conveyor belts 12,13 are driven by a common motor15.

The workpiece carrier 11 is encompassed by a frame 16 fixed to themachine and comprising a lower bar 17 arranged below workpiece carrier11 and an upper bar 18 arranged in parallel to lower beam 17. Along eachbar, a carriage 19,20 is arranged to be displaced in the Y-direction.The two carriages 19,20 are driven in synchronism with each other, thusassuming always the same positions in the Y-direction.

On each of the carriages 19,20, a bandknife rotating device 21 ismounted, having a slot for passing the bandknife 22 therethrough. Thesebandknife rotating devices 21 guide the bandknife 22 and are controlledin such a manner that the face of bandknife 22 in the cutting strand 23can be adjusted to a desired cutting angle, e.g. to the tangent angle ofthe cutting contour to be generated.

A bandknife pulley 30 is supported on the upper carriage 20, and abandknife pulley 31 is supported on the lower carriage 19. Frombandknife pulley 31, the bandknife 22 extends to a fixed bandknifepulley 32 supported on worktool carrier 16 and driven by a motor 24.From bandknife pulley 32, arranged at the same height as bandknifepulley 31, the bandknife 22 extends vertically upwards to a furtherbandknife pulley 33 supported on worktool carrier 16 where the bandknife22 is deflected by substantially 90°. From bandknife pulley 33, thebandknife 22 extends above bandknife pulley 30 to a fifth bandknifepulley 34 arranged at the end of upper bar 18. Between bandknife pulleys33 and 34, the carriage 20 is movable in the Y-direction.

FIG. 3 illustrates the moving path of the bandknife pulley 22 in a givenY-position of the cutting strand 23. In the cutting strand 23, thebandknife 22 is moved downwards from above in the direction of thearrow. The cutting strand 23 together with the bandknife portions25,26,27 forms a first rectangular loop 28. Bandknife portion 27 isjoined by a bandknife portion 29 leading to bandknife pulley 34, whichbandknife portion 29 together with bandknife portion 35 leading frombandknife pulley 34 to bandknife pulley 30, forms the second loop 36which constitutes a compensating loop. Loop 36 starts from the upperleft corner of loop 28 in an outward direction, and its verticaldimension (loop height) is considerably smaller than that of first loop28 and is substantially restricted to the diameter of bandknife pulley34.

Lower bandknife portion 35 of loop 36 is guided horizontally tobandknife pulley 30 from below. This bandknife pulley 30 guides thebandknife 22 therearound at a looping angle of substantially 270° sothat the bandknife 22 runs around bandknife pulley 30 and then moves ina downward direction to join the cutting strand 23. To prevent acollision of bandknife portions 27 and 29 with the bandknife portionguided around bandknife pulley 30, bandknife pulley 33 is suitablyarranged somewhat higher than bandknife pulley 30.

FIG. 5 is a view of bandknife pulley 30. While all other bandknifepulleys are arranged in a common plane, bandknife pulley 30 is orientedat an inclination to this plane so that the outgoing cutting strand 23will not collide with the incoming bandknife portion 35.

Each bandknife pulley is formed with an outwardly curved peripheralsurface to keep the bandknife 22 from sliding off the bandknife pulley.Preferably, the peripheral surface is part of a spherical surface. Thus,the bandknife pulley can be imagined as a cut-out slice from a completespherical body.

From FIGS. 3 and 4, it is evident that the two loops 28,36 form a closedcirculation path for the bandknife and that, when the position of thecutting strand 23 is changed in the Y-direction, the length of thiscirculation path will still remain constant. To lend the bandknife therequired bandknife tension in the longitudinal direction, bandknifepulley 34 is engaged by a tensioning device 37.

The bandknife pulleys 30,31,32,33 of the first loop 28 are generallyarranged in the configuration of a rectangle, and the bandknife pulleys30,33,34 are located substantially at the same height.

The bandknife circulation path can be realized with only five bandknifepulleys without excluding the possibility to provide a larger number ofbandknife pulleys, if required. It is imperative that the bandknife oneach of the bandknife pulleys of its circulation path will be bent inthe same direction, thus avoiding alternating bending directions.

Although a preferred embodiment of the invention has been specificallyillustrated and described herein, it is to be understood that minorvariations may be made in the apparatus without departing from thespirit and scope of the invention, as defined the appended claims.

We claim:
 1. A contour cutting machine comprising a circulating endlessbandknife (22) guided around a plurality of bandknife pulleys (30-34)and extending in two loops (28, 36) merging into each other, a firstloop (28) being guided around two fixed bandknife pulleys (32, 33) andaround two displaceable bandknife pulleys (30, 31) which aresubstantially simultaneously displaceable, and a second loop (36) beingguided around a further bandknife pulley (34), characterized in thatsaid endless bandknife (22) is guided at a looping angle ofsubstantially 270° around one pulley (30) of the displaceable bandknifepulleys (30, 31) which connects the two loops (28, 36), and allbandknife pulleys (30-34) being contacted by the same surface of theendless bandknife (22).
 2. The contour cutting machine according toclaim 1, characterized in that said one displaceable bandknife pulley(30) connecting said two loops (28, 36) is oriented at an inclinationrelative to the plane of the other bandknife pulleys so as to guide anincoming bandknife portion (35) of said endless bandknife (22) and anoutgoing cutting strand (23) of said endless bandknife (22) past eachother without collision.
 3. The contour cutting machine according toclaim 2, characterized in that the plurality of bandknife pulleys(30-34) are supported on a worktool carrier (16), and two conveyor belts(12, 13), separated from each other by a gap (14) for the passage of theendless bandknife (22), are provided for supporting material to be cut.4. The contour cutting machine according to claim 1, characterized inthat said two displaceable bandknife pulleys (30, 31) are arranged onsynchronously moveable carriages (20, 19) which are each provide withrotating means (21) for varying a plane of the cutting strand (23) ofthe endless bandknife (22).
 5. The contour cutting machine according toclaim 4, characterized in that the plurality of bandknife pulleys(30-34) are supported on a worktool carrier (16), and two conveyor belts(12, 13), separated from each other by a gap (14) for the passage of theendless bandknife (22), are provided for supporting material to be cut.6. The contour cutting machine according to claim 4, characterized inthat said two displaceable bandknife pulleys (30, 31) are arranged onsynchronously moveable carriages (20, 19) which are each provide withrotating means (21) for varying a plane of the cutting strand (23) ofthe endless bandknife (22).
 7. The contour cutting machine according toclaim 1, characterized in that the plurality of bandknife pulleys(30-34) are supported on a worktool carrier (16), and two conveyor belts(12, 13), separated from each other by a gap (14) for the passage of theendless bandknife (22), are provided for supporting material to be cut.8. The contour cutting machine according to claim 1 characterized inthat said endless bandknife (22) includes an incoming bandknife portionand an outgoing bandknife portion which cross each other at a pointsubstantially diametrically opposite the midpoint of the substantially270° looping of the endless bandknife (22) about said one pulley (30).9. The contour cutting machine according to claim 8 wherein saidsubstantially 270° looping about said one pulley (30) defines in parteach of said two loops (28, 36).
 10. The contour cutting machineaccording to claim 9 wherein said one pulley (30) is in a plane inclinedto a plane of the remaining pulleys.
 11. The contour cutting machineaccording to claim 8 wherein said one pulley (30) is in a plane inclinedto a plane of the remaining pulleys.
 12. The contour cutting machineaccording to claim 1 wherein said substantially 270° looping about saidone pulley (30) defines in part each of said two loops (28, 36).
 13. Thecontour cutting machine according to claim 12 wherein said one pulley(30) is in a plane inclined to a plane of the remaining pulleys.